Telephone station equipment has traditionally relied on receiving its power from a telephone central office which provides a supply of voltage whose magnitude, source impedance, and reliability are known and controllable. The advantages of such an arrangement are well known in view of periodic commercial power outages, during which time telephone communications, particularly emergency services, have not been interrupted for lack of power. A disadvantage of this arrangement, however, has been the fact that the maximum power that can be relied on is relatively small due to the fact that the wires connecting the telephone to the central office are resistive, and may be quite long (many miles). Public coin telephone equipment is no exception to the tradition of receiving its power from a central office and must operate reliably at low power levels.
Mechanical coin chutes have been used for years in coin telephone equipment. They perform the job of authenticating and accepting coins without electrical power so that all of the available power is at the disposal of the circuits used for signaling and speech. Unfortunately, mechanical coin chutes are bulky, expensive, and account for at least 50% of the problems associated with the equipment to which they are attached. Recently, electronic means have been used to simplify coin chute design, improve reliability and reduce cost. However, electronic coin chutes (ECCs) consume power in carrying out their job of authenticating and accepting coins of various denominations, and it is not desirable to introduce batteries or commercial power (115 VAC) into coin telephone equipment for a variety of reasons.
U.S. Pat. No. 4,848,556 discloses a Low Power Coin Discrimination Apparatus which uses a battery to power a piezoelectric transducer that measures the mass of the coin, and a photoelectric sensor that measures its area. The discriminator automatically returns to a lower power state once it has completed the discrimination process. However, since the available current is severely limited, powering such discrimination apparatus may not be possible--particularly when relatively large amounts of current are required. Indeed, a single light emitting diode may need the entire available current to be effective. Further, since it is neither convenient nor cost effective to use batteries when powering coin telephone equipment, the techniques disclosed in the above patent are not directly applicable to situations in which peak power is severely limited.
British Patent GB 2078466A discloses a microprocessor-controlled, coin-operated telephone that uses a microprocessor to activate and de-activate various parts of a pay phone. This particular telephone, however, relies on the use of light emitting diodes and opto-electronic sensors to monitor the location of coins within the chute. In order to supply the needed power, a rechargeable Nickel-Cadmium battery is used. However, when the use of batteries is permitted, strategies are developed for reducing overall power usage which are not appropriate when minimizing peak power consumption.
One technique for reducing peak power consumption uses energy storage devices that slowly build-up electric charge over a long period of time. Unfortunately, when a telephone station is in an "on-hook" state, only an insignificant amount of current is present on the telephone line. And when the telephone station is in an "off-hook" state, although more current is available, any delay in operation due to the build-up of electric charge is undesirable.